A process of performing hot rolling using a high temperature solidified cast part in a continuous casting device is currently widely used, due to equipment costs and operating costs thereof being more inexpensive than those of conventional equipment and processes.
Also, a discontinuous process capable of performing hot rolling separately from continuous casting, while continuously undertaking continuous casting and the hot rolling can also be performed. This discontinuous process is disclosed in detail in published Korean Patent No. 1990-7001437.
That is, as illustrated in FIGS. 1A and 1B, a continuous hot rolling mode of continuously performing continuous casting and hot rolling, and a discontinuous hot rolling mode of discontinuously performing continuous casting and hot rolling can be used, respectively.
Here, FIG. 1A illustrates a facility 1′ capable of performing continuous hot rolling. When a cast part 2′ having a constant thickness is generated in a continuous casting device 100′, the cast part 2′ is first hot-rolled in a first hot-rolling unit 210′, the temperature is retained in a heat insulating means 320′, and a steel sheet 2a′ that presses the cast part 2′ down is heated by heaters 310′ to a temperature for hot-rolling to finish the final hot rolling in a second hot rolling section 220. The steel sheet 2a′, after finishing hot rolling, is cut with a third cutter 430′ and wound with a rewinder R to produce a hot-rolled steel sheet 2a′. 
Meanwhile, FIG. 1B illustrates facility 1′ capable of performing discontinuous hot rolling. When the cast part 2′ having a constant thickness is produced in the continuous casting device 100′, the cast part 2′ is first hot-rolled in the first hot-rolling unit 210′ and is cut with the first cutter 411′ before moving to the heat insulating means 320′, thereby performing hot rolling without being restricted to the casting speed of the continuous casting device 100′.
Here, the cutting steel sheet 2a′ provided by cutting the steel sheet 2a′ that presses the cast part 2′ down is wound, and is then provided to finish the final hot rolling in the second hot rolling section 220′ again. After being heated by the heater 310′ to the temperature for hot-rolling, the cutting steel sheet 2a′ is finally hot-rolled, is wound by the rewinder R and is produced as a hot-rolled steel sheet 2a′. 
However, when performing such a hot-rolling process, since the hot rolling is performed by the first hot rolling section 210′ in a state in which the temperature distribution of the cast part 2′ provided by being produced in the continuous casting device 100′ is uneven, there may be a problem of a reduction in the quality of the hot-rolled steel sheet 2a′. 
Further, in the case of switching from the discontinuous hot rolling mode to the continuous hot rolling mode, when the cast part 2 provided by being produced in the continuous casting device 100′ is depressed into the first hot rolling section 210′, the speed of the continuous casting device 100′ is restricted, thereby causing a problem of forming a strap on the cast part 2′.
To solve this problem, conventionally, the hot rolling process has been sequentially performed by gradually reducing an interval between top and bottom rolls of a plurality of hot rolling rolls of the first hot rolling section 210′. However, a transition zone in which the thickness is reduced has been generated at a tip portion of the sequentially hot-rolled steel sheet 2a′, thereby causing another problem of lowering the quality of the produced hot-rolled steel sheet 2a′. 
Therefore, there is a need for research into a hot rolling apparatus, and an apparatus and a method for continuous casting and hot rolling to solve the above-mentioned problems.